The objectives of this contract are to design, synthesize and test peptide antagonists which have very low histamine releasing properties (equivalent to LHRH, or less) and which completely inhibit ovulation in rats, s.c., at one-tenth the dose of the most potent antagonists currently available, such as Nal-Glu or Antide. Such antagonists should, desirably, also be devoid of (or have minimal) ancillary endocrine, central nervous system, cardiovascular and other side effects.